1. Field of Invention
The present invention relates to a solid powder trap having a device capable of monitoring the degree of powder accumulation inside the device. More particularly, the present invention relates to a solid power trap having a device that measures the change in magnetic flux due to the accumulation of powder and hence informs the operator the degree of powder accumulation inside the trap.
2. Description of Related Art
A solid powder trap is a device frequently used to filter away suspended solid particles in a gaseous mixture. Powder traps may be employed in many engineering projects, such as inside a tunnel for trapping dust particles, for example. The air filter inside an air conditioner for filtering dust particles inside a house is also regarded as a kind of solid power trap. If the solid particles are non-toxic, the particles can simply be expelled from the generating source to the atmosphere using an exhaust fan or a pump. However, if the solid particles can lead to environmental pollution, the solid particles must first be collected and then disposed by other means. There are many methods of trapping solid particles including filtering, adsorption or electrostatic attraction. Proper method for catching the solid particles depends very much on the particle size and the particle characteristics. In general, it does not matter what method is used to catch the solid particles. Any device capable of filtering solid particles can be regarded as a solid powder trap.
In semiconductor fabrication, solid powder traps are often used alongside processing stations such as a chemical vapor deposition (CVD) station or an etcher, for example. When these processing stations are in operation, a large amount of reaction products (one example is aluminum chloride AlCl3) is usually generated. Some of these reaction products may form a solid powder at atmospheric temperature. If the solid powder is not removed quickly enough, it may accumulate inside the reaction chamber of the processing station and become a source of impurities. Moreover, if the unwanted impurities are allowed to accumulate, quality of the finished product may be affected.
In general, the solid powder is removed from the reaction chamber using a powder trap. FIG. 1 is a structural diagram showing a conventional solid powder trapping system. As shown in FIG. 1, the solid powder trapping system includes an air pump 100 that connects with a reaction chamber or station (not shown in the figure). The gaseous mixture is imput out of the chamber and passed into a pipeline 102. A solid powder trap 104 is attached to the end of the pipeline 102. Therefore, as the air mixture is passed into the solid powder trap 104, solid powder suspended in the air separates out. Finally, the filtered air is expelled into a local scrubber through another pipeline 106.
For the above type of solid powder trap, there is no sensor for detecting the degree of powder accumulation inside the trap. Therefore, if one has to determine the degree of powder accumulation inside the trap, the only way is to open the trap and investigate the state of powder accumulation inside. Every other method is mostly guesswork. However, without a general knowledge of the degree of powder accumulation inside the trap, the only way to maintain operational efficiency of the trap is to clean it at a fixed time interval. Therefore, over-cleaning or under-cleaning of the trap is likely, which lead to a waste of labor and resources. Moreover, when particle concentration inside a reaction chamber is too high or the pumping efficiency too low, it is difficult to pinpoint the problem. One must check the pump and the solid powder trap, t hereby extending the idle time o f th e machine and hence lowering its productivity.
In light of the foregoing, there is a need to provide a device for monitoring the degree o f powder accumulation inside the solid powder trap.
Accordingly, the purpose of the present invention is to provide a device for monitoring the degree of powder accumulation inside a solid powder trap. The device utilizes the dependency of magnetic flux on the amount of powder accumulated inside the powder trap for estimating the degree of powder accumulation and then using that information to schedule the appropriate cleaning or maintenance period. In particular, the cleaning operation can be scheduled during machine stop time so that machine down time is reduced and productivity is increased.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a solid powder trapping system having a display device showing the degree of powder accumulation. The solid powder trapping system includes a solid powder trap, a magnetic flux sensor and a display device. The solid powder trap is a column for receiving a gaseous mixture from a reaction chamber. After trapping the solid powder inside the gaseous mixture, the filtered mixture is passed out. The magnetic flux sensor is installed inside the solid powder trap for determining the state of powder accumulation by sensing the amount of magnetic flux going through a magnetic flux circuit. Any changes in magnetic flux measurement are displayed on a display device. By reading the value from the display device, the degree of powder accumulation inside the trap can be estimated.
In addition, the magnetic flux sensor includes a U-shaped iron core, a first inductive coil and a second inductive coil. The first inductive coil is wound around one arm of the iron core. An alternating current is applied to the first inductive coil. The second inductive coil is wound around the opposite arm of the iron core. The second inductive coil is connected to the display device. As current flows into the first inductive coil generates a magnetic flux in the iron core. The magnetic flux passes through the iron core in the first arm, through the accumulated solid powder and arrives at the iron core on the second arm. Hence, the second inductive coil is able to pick up the magnetic flux.
Furthermore, the external portion of the iron core is surrounded by ceramic material. The ceramic enclosure is amied to minimize the loss of magnetic flux during from along the iron core.
The display device can be a voltmeter. By tapping the magnetic flux through the second arm of the iron core, a current is generated in the second inductive coil. The current is then converted into a voltage reading that indicates the degree of powder accumulation inside the trap.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.